Resin composition and sheet for optical screen

ABSTRACT

A resin composition comprising (A) an elastomeric copolymer which comprises styrene monomeric units and diene monomeric units, and (B) a copolymer which comprises styrene monomeric units and (meth)acrylate monomeric units, which has a saturated water absorption of 0.8% or less at a temperature of 60° C. and a relative humidity of 90%, a flexural modulus of at least 1,800 MPa, a notched Izod impact strength of at least 2 kJ/m 2 , a total light transmittance of at least 85% and a haze value of 5% or less when providing a sheet having a thickness of 2 mm, and a Vicat softening point of at least 90° C. This resin composition can suitably be used as a base material of a sheet for a screen which has good transparency, suffers from less deformation such as warp or deflection, and is hardly cracked or chipped.

This application is the national phase under 35 U.S.C. § 371 of PCTInternational Application No. PCT/JP02/00367 which has an Internationalfiling date of Jan. 21, 2002, which designated the United States ofAmerica.

FIELD OF THE INVENTION

The present invention relates to a resin composition and a sheet for anoptical screen comprising the same as a base material.

BACKGROUND ART

An optical screen such as a transmission type screen of a projectiontelevision usually comprises a lens sheet such as a Fresnel lens sheetor a lenticular lens sheet. In these years, a front panel may beattached to the surface of such a lens sheet for protecting the lenssheet.

As a base material of such a sheet for an optical screen, an acrylicresin is mainly used from the viewpoint of transparency. For example,JP-A-1-128059 discloses a lens sheet comprising an acrylic resin towhich a methyl methacrylate base multilayer rubber is added.JP-A-9-302176 and JP-A-9-302177 disclose a lens sheet comprising amethyl methacrylate-styrene copolymer resin. Furthermore,JP-A-2000-66307 discloses a lens sheet comprising a methylmethacrylate-styrene copolymer resin to which a butadiene base graftrubber is added.

However, the lens sheets disclosed in JP-A-1-128059 and JP-A-2000-66307have problems such that they tend to warp or deflect when they are used,stored or transported. The lens sheets disclosed in JP-A-9-302176 andJP-A-9-302177 have problems such that they tend to be cracked or chippedwhen they are processed or installed.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a resin materialsuitable for use as a base material of a sheet for a screen which hasgood transparency, suffers from less deformation such as warp ordeflection, and is hardly cracked or chipped.

Accordingly, the present invention provides a resin compositioncomprising (A) an elastomeric copolymer which comprises styrenemonomeric units and diene monomeric units, and (B) a copolymer whichcomprises styrene monomeric units and (meth)acrylate monomeric units,the composition having the following properties (1) to (5):

-   -   (1) a saturated water absorption of 0.8% or less at a        temperature of 60° C. and a relative humidity of 90%;    -   (2) a flexural modulus of at least 1,800 MPa;    -   (3) a notched Izod impact strength of at least 2 kJ/m²;    -   (4) a total light transmittance of at least 85% and a haze value        of 5% or less when providing a sheet with a thickness of 2 mm;        and    -   (5) a Vicat softening point of at least 90° C.

Furthermore, the present invention provides a sheet for an opticalscreen comprising a resin composition of the present invention as a basematerial.

In addition, the present invention provides a method for producing ascreen for an optical screen comprising the step of cutting a sheetcomprising a resin composition of the present invention as a basematerial so as to apply cutting blades to the respective surfaces of thesheet.

Embodiments for Working the Invention

Hereinafter, the present invention will be explained in detail. Herein,the term “(meth)acrylates” is intended to mean esters of acrylic acidand/or esters of methacrylic acid.

The resin composition of the present invention comprises (A) anelastomeric (rubber) copolymer which comprises styrene monomeric unitsand diene monomeric units, and (B) a copolymer which comprises styrenemonomeric units and (meth)acrylate monomeric units, and the particles ofthe elastomeric copolymer (A) are usually dispersed in a continuousphase of the copolymer (B).

The styrene monomer (monomeric unit) which constitutes the elatomericcopolymer (A) means styrene or a styrene derivative. Examples of thestyrene monomer include styrene, alkyl-substituted s tyrenes (e.g.o-methylstyrene, p-methylstyrene, m-methylstyrene, 2,4-dimethylsytrene,p-ethylstyrene, p-tert-butylstyrene, α-methylstyrene,α-methyl-p-methylstyrene, etc.), halogen-substituted styrenes (e.g.o-chlorostyrene, p-chlorostyrene, etc.), and so on. Among them, styreneis preferable. The styrene monomers may be used as a mixture of two ormore of them, if desired.

Examples of the diene monomer(monomeric unit) which constitutes theelastomeric copolymer (A) include butadiene, 2-methylbutadiene,2,3-dimethylbutadiene, etc. Among them, butadiene is preferable. Thebutadiene monomers may be used as a mixture of two or more of them, ifdesired.

Besides the styrene monomer and the butadiene monomer, the elastomericcopolymer (A) may optionally comprise other monomer. Examples of suchoptional monomers include (meth)acrylates (e.g. methyl acrylate, ethylacrylate, butyl acrylate, cyclohexyl acrylate, phenyl acrylate, benzylacrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, methylmethacrylate, ethyl methacrylate, butyl methacrylate, cyclohexylmethacrylate, phenyl methacrylate, benzyl methacrylate, 2-ethylhexylmethacrylate, 2-hydroxyethyl methacrylate, etc.), unsaturated nitriles(e.g. acrylonitrile, methacrylonitrile, etc.), unsaturated amides (e.g.acrylamide, diacetoneacrylamide, etc.), unsaturated acids (e.g. acrylicacid, methacrylic acid, etc.), unsaturated imides (e.g. phenylmaleimide,cyclohexylmaleimide, etc.), unsaturated acid anhydrides (e.g. maleicanhydride, etc.), and so on.

Examples of the styrene monomer which constitutes the copolymer (B) maybe the same as those exemplified for the styrene monomer whichconstitutes the elastomeric copolymer (A). Among them, styrene ispreferable.

Examples of the (meth)acrylate monomer(styrene monomeric unit) whichconstitutes the copolymer (B) may be the same as those exemplifiedabove. Among them, methyl methacrylate is preferable.

Besides the styrene monomer and the (meth) acrylate monomer, thecopolymer (B) may optionally comprise other monomer. Examples of suchoptional monomers include above-exemplified unsaturated nitriles,unsaturated amides, unsaturated acids, unsaturated imides, unsaturatedacid anhydrides, and so on.

The resin composition of the present invention should have a saturatedwater absorption of 0.8% or less at a temperature of 60° C. and arelative humidity of 90%. When the saturated water absorption exceeds0.8%, a screen produced from the resin composition tends to greatly warpdue to the dimensional change caused by water absorbed, and to cause thedeterioration of images due to defocusing. The saturated waterabsorption is preferably 0.7% or less.

The resin composition of the present invention should have a flexuralmodulus of at least 1,800 MPa. When the flexural modulus less than 1,800MPa, a screen produced from the resin composition tends to be deflectedand may have insufficient self-supporting properties. The flexuralmodulus is preferably at least 1,900 MPa.

The resin composition of the present invention should have a notchedIzod impact strength of at least 2 kJ/m². When the notched Izod impactstrength is less than 2 kJ/m², a sheet or a screen produced from theresin composition tends to be easily cracked or chipped when it isprocessed to produce a screen or the screen is installed. The notchedIzod impact strength is preferably at least 2.5 kJ/m².

Furthermore, when providing a sheet having a thickness of 2 mm, theresin composition of the present invention should have a total lighttransmittance of at least 85% in the direction of the thickness of thesheet, and a haze value of 5% or less. When the total lighttransmittance is less than 85%, the luminance of the screen producedfrom the resin composition may be insufficient. When the haze valueexceeds 5%, the face of the screen may lose the clearness.

Finally, the resin composition of the present invention should have aVicat softening point of at least 90° C. When the Vicat softening pointis lower than 90° C., a screen produced from the resin composition tendsto be thermally deformed, when a temperature rises relatively highduring the storage or transportation of the screen. The Vicat softeningpoint is preferably at least 95° C.

The resin composition, which comprises the elastomeric copolymer (A) andthe copolymer (B) and has the desired properties, may be prepared byusing the elatomeric copolymer (A), the styrene monomer, the(meth)acrylate monomer and optional other monomer or monomers as the rawmaterials, and mixing and polymerizing them with suitably adjusting thekinds and amounts of the monomers and polymerization conditions. In thecourse of the polymerization, the styrene monomer, the (meth)acrylatemonomer and the optional other monomer are copolymerized to produce thecopolymer (B), while a portion of the styrene monomer, the (meth)acrylate monomer and the optional other monomer may optionally begrafted on the elastomeric copolymer (A).

The elastomeric copolymer (A) preferably comprises 5 to 50% by weight ofthe styrene monomeric units and 50 to 95% by weight of the dienemonomeric units, more preferably 10 to 45% by weight of the styrenemonomeric units and 55 to 90% by weight of the diene monomeric units,and most preferably 15 to 40% by weight of the styrene monomeric unitsand 60 to 85% by weight of the diene monomeric units. As the amount ofthe diene monomeric units in the elastomeric polymer (A) is increased,the notched Izod impact strength of the resin composition can beincreased.

The elastomeric polymer (A) may be a random copolymer or a blockcopolymer. Among them, the random copolymer is preferable in view of thebalance between the total light transmittance of the resin compositionand the color of the transmitted light. The elastomeric copolymer may beprepared by solution polymerization or emulsion polymerization. In viewof the decrease of the saturated water absorption of the resincomposition, the elastomeric copolymer is preferably prepared bysolution polymerization.

The amounts of the monomers in the raw materials are such that, eachbased on the whole monomers, that is, the total weight of the styrenemonomer, the (meth)acrylate monomer and the optional other monomer,preferably the styrene monomer is 25 to 65% by weight, the(meth)acrylate monomer is 35 to 75% by weight and the optional othermonomer is 0 to 40% by weight, more preferably the styrene monomer is 30to 60% by weight, the (meth)acrylate monomer is 40 to 70% by weight andthe optional other monomer is 0to 30% by weight, and most preferably thestyrene monomer is 35 to 55% by weight, the (meth)acrylate monomer is 45to 65% by weight and the optional other monomer is 0 to 20% by weight.As the amount ratio of the styrene monomer to the total weight of themonomers is increased, the saturated water absorption of the resincomposition can be decreased. On the other hand, as the amount ratio ofthe (meth)acrylate monomer is increased, the Vicat softening point ofthe resin composition can be heightened. In view of the increase in thetotal light transmittance and the decrease in the haze value of theresin composition, the amounts of the monomers in the raw materials arepreferably adjusted so that there is small difference in the refractiveindex between the copolymer (B) prepared and the elastomeric copolymer(A).

The proportions of the amount of elastomeric copolymer (A) and the totalamount of the monomers in the raw materials are such that, based on thesum of the weights of the elastomeric copolymer (A) and the monomers,preferably the former is 1 to 20% by weight and the latter is 80 to 99%by weight, more preferably the former is 2 to 18% by weight and thelatter is 82 to 98% by weight, and most preferably the former is 3 to15% by weight and the latter is 85 to 97% by weight. As the proportionof the former is increased, the saturated water absorption of the resincomposition can be decreased while the notched Izod impact strength canbe increased. On the other hand, when the proportion of the latter isincreased, the flexural modulus of the resin composition can beincreased and the Vicat softening point can be heightened.

To polymerize the mixture of the raw materials, preferably they arepartially polymerized by bulk polymerization and then the partiallypolymerized material is further polymerized by cast polymerization orsuspension polymerization as disclosed, for example, in U.S. Pat. No.4,287,317 (corresponding to JP-B-62-13968), or they are polymerized bycontinuous bulk polymerization and then the unreacted monomers areremoved and recovered.

In each polymerization method, azo compounds or organic peroxides may beused as radical polymerization initiators. In addition, chain transferagents may be used to control the polymerization rate, the molecularweight, the rubber dispersion state, etc. The raw materials may be mixedall at once, or they may be mixed portion by portion. In the case of theportion-by-portion mixing, for example, the elastomeric copolymer (A)and a portion of the monomers are mixed and partially polymerized, andthen the partially polymerized product and the remainder of the monomersare mixed and polymerized.

The resin composition of the present invention has excellent propertiesand can preferably be used as a material of various resin moldedarticles. When various resin molded articles are produced using theresin composition of the present invention, the resin composition maycontain, if desired, at least one of conventional additives such as heatstabilizers, antioxidants, light stabilizers, UV ray absorbers,colorants, plasticizers, mold release agents, lubricants,light-diffusing agents, etc. These additives may be added when the resincomposition is prepared by polymerization. Alternatively, the additivesmay be added to the resin composition, when it is pelletized.

The resin composition of the present invention can be suitably used as amaterial of an optical member, in particular, as a base material of asheet for an optical screen such as a transmission type screen of aprojection television. Examples of the sheet for the optical screeninclude lens sheets such as a Fresnel lens sheet and a lenticular lenssheet, front panels, etc.

The Fresnel lens sheet may be produced by cast molding, or by pressmolding a sheet as an original sheet, which is produced by cast moldingor extrusion molding, to impart the Fresnel lens shape to the sheet, orby curing a UV-curable resin on the surface of a sheet to form a Fresnellens shape.

The lenticular lens sheet may be produced by extrusion molding or castmolding, or by press molding a sheet as an original sheet to impart thelenticular lens shape to the sheet, or by adhering a film of aUV-curable resin having a lenticular lens shape on its surface to asheet as an original sheet.

The front panel may be produced by extrusion molding or cast molding,and further providing a surface treatment such as a hard coating or alow-reflection coating to a sheet.

In the production of the sheet for the optical screen such as theFresnel lens sheet, the lenticular lens sheet or the front panel, thesheet is usually cut to a desired size in the final step. In this case,it is preferable from the viewpoint of productivity and costs to employa method comprising applying cutting blades to the respective surfacesof the sheet in a direction substantially perpendicular to the surfaceof the sheet to cut the sheet, that is, a so-called press cuttingmethod. In this method, if the impact strength of the sheet isinsufficient, the sheet tends to be cracked or chipped. When a sheetcomprising the resin composition with a high notched Izod impactstrength of at least 2 kJ/m² is used according to the present invention,it is less cracked or chipped. From such a viewpoint, the notched Izodimpact strength is preferably at least 3 kJ/m², more preferably at least4 kJ/m², and most preferably at least 5 kJ/m².

In particular, when a Fresnel lens sheet is produced, among theabove-described methods, the method comprising curing a UV-curable resinon the surface of a sheet as an original sheet to form a Fresnel lensshape is preferable in view of the productivity and costs. In this case,the thickness of the cured resin layer of the Fresnel lens shape isusually form 100 to 300 nm. In this method, an extra cured resin layer,which extends beyond the periphery of the sheet in the form of a burr,is often formed with a thickness of several millimeters. Such an extramarginal part is preferably removed by press cutting. In this presscutting process, cutting blades are applied to the surface having thecured resin layer of the sheet and also to the opposite surface of thesheet. Since the former surface is usually harder than the lattersurface, the cutting is actually carried out with propagating a notchformed on the latter surface toward the former surface. Therefore, sucha press cutting process is carried out under conditions under which thesheet is easily cracked or chipped. However, when the sheet comprisesthe resin composition of the present invention, it is hardly cracked orchipped.

In the case of an optical screen comprising a plurality of sheets, forexample, an optical screen consisting of a Fresnel lens sheet, alenticular lens sheet and a front panel, at lease one of those sheets,preferably, all the sheets are sheets comprising the resin compositionof the present invention.

EXAMPLES

Hereinafter, the examples of the present invention are explained, butthose examples do not limit the scope of the present invention.

The properties of the resin sheets obtained were measured as follows:

(1) Saturated Water Absorption (%)

A test piece was cut out from a resin sheet having a thickness of 2 mmand vacuum dried at 80° C. overnight, and then the dried test piece wasweighed. This weight is referred to as “dry test piece weight”. Then,the dried test piece was placed in a thermo-hygrostat apparatusmaintained at 60° C. and 90% RH until the weight became constant. Thisconstant weight reached is referred to as “water-saturated test pieceweight”.

From the dry test piece weight and the water-saturated test pieceweight, a saturated water absorption was calculated according to thefollowing equation:Saturated water absorption (%)=100×[(water-saturated test pieceweight)−(dry test piece weight)]/(dry test piece weight)

(2) Flexural Modulus (MPa)

A test piece cut out from a resin sheet having a thickness of 2 mm, anda flexural modulus was measured according to JIS K 7203 (1995).

(3) Notched Izod Impact Strength (KJ/m²)

A test piece cut out from a resin sheet having a thickness of 2 mm, anda notched Izod impact strength was measured according to JIS K 7110(1999).

(4) Total Light Transmittance (%) and haze value (%)

A test piece cut out from a resin sheet having a thickness of 2 mm, atotal light transmittance and a haze value were measured according toJIS K 7105 (1981).

(5) Vicat Softening Point (° C.)

A test piece cut out from a resin sheet having a thickness of 2 mm, aVicat softening point was measured according to JIS K 7206 (1991).

(I) Warp

A test sample of 20 cm×30 cm was cut out from a resin sheet having athickness of 2 mm, and an aluminum foil was adhered to one surface ofthe sample with an adhesive. Then, the sample with the aluminum foil wasplaced in a thermo-hygrostat apparatus maintained at 60° C. and 90%RH(relative humidity) for 24 hours. Then, the degree of warping of thesample was visually evaluated.

(II) Deflection

A test sample of 20 cm×30 cm was cut out from a resin sheet having athickness of 1 mm and was placed and fixed vertically with the side of20 cm as a base. Then, the degree of deflection of the sample wasvisually evaluated.

(III) Cracking and Chipping

A test sample of 20 cm×30 cm was cut out from a resin sheet having athickness of 2 mm, and a nick was formed with an acryl cutter inparallel with the direction of the 20 cm side. Then, the sample wasbroken with hands along the nick, and the presence of cracking orchipping on the broken face was visually inspected.

(IV) Clearness of Image

A test sample of 20 cm×30 cm was cut out from a resin sheet having athickness of 2 mm and attached on the front face of the screen of aprojection television. Then, the degree of clearness of an imageprojected on the screen was visually judged.

(V) Thermal Deformation

A test sample of 20 cm×30 cm was cut out from a resin sheet having athickness of 2 mm and maintained at 80° C. for one week. Then, thedeformation of the sample was visually inspected.

As an elastomeric copolymer, the following copolymers were used:

(a) Styrene-butadiene random copolymer (styrene:butadiene=25:75 byweight) (TUFDENE L 208 A available from Japan Elastomer Company)

(b) Styrene-butadiene block copolymer (styrene:butadiene=40:60 byweight) (NS 312S available from ZEON CORPORATION.)

(c) Butadiene rubber (ASAPRENE 730 AS available from Japan ElastomerCompany)

(d) Styrene-butadiene random copolymer (styrene:butadiene=20:80 byweight) (NS 218 S available from ZEON CORPORATION.)

Examples 1-3 And Comparative Examples 1-4

Elastomeric copolymers, monomers and polymerization initiators shown inTable 1 were mixed in amounts shown in Table 1 and then partiallypolymerized with a two-stage agitation type continuous reactor at 150°C. at a predetermined residence time (360 seconds in Examples 1-3 andComparative Examples 1 and 4; 225 seconds in Comparative Examples 2 and3).

To the partially polymerized products (85 parts by weight), monomersshown in Table 2 in amounts shown in Table 2, 0.1 part by weight of2,2′-azobis(2,4-dimethylvalleronitrile) as a polymerization initiator,0.3 part by weight of tert-amyl peroxy2-ethylhexanoate as apolymerization initiator and 0.1 part by weight of tert-dodecylmercaptanas a chain transfer agent were added. The mixture was charged in each oftwo cells, which were constructed with a pair of glass plates and agasket with a gap distance of 1 mm and 2 mm, respectively, and heated ina water bath kept at 80° C. for 3 hours and then in an air oven kept at120° C. for 1 hour to complete the polymerization. Thereby, resin sheetsrespectively having thicknesses of 1 mm and 2 mm were obtained.

A weight ratio of the elastomeric copolymer and the monomers (styreneand methyl methacrylate) and a weight ratio of styrene to methylmethacrylate in total are shown in Table 2.

The properties of the resin sheet having a thickness of 2 mm aresummarized in Table 3, while the results of the evaluations of the resinsheet having a thickness of 1 mm or 2 mm are summarized in Table 4.

Comparative Example 5

A styrene-methyl methacrylate copolymer (a weight ratio of styrene tomethyl methacrylate=40:60) (MS 600 available from Nippon Steel ChemicalCo., Ltd.) was molded with an extrusion molding machine to obtain resinsheets respectively having thicknesses of 1 mm and 2 mm. The propertiesof the resin sheet having a thickness of 2 mm are summarized in Table 3,while the results of the evaluations of the resin sheet having athickness of 1 mm or 2 mm are summarized in Table 4.

TABLE 1 Polymerization initiator Monomer Benzyl Lauryl Styrene Methylperoxide peroxide Elastomeric (parts methacrylate (parts (parts Examplecopolymer by (parts by by by No. Kind PBW weight) weight) weight)weight) Ex. 1 (a) 5.0 36.1 58.9 0.016 0.131 Ex. 2 (a) 5.0 36.1 58.90.016 0.131 Ex. 3 (b) 5.0 52.2 42.8 — 0.362 C. Ex. 1 (a) 5.0 36.1 58.90.016 0.131 C. Ex. 2 (c) 5.0 11.4 83.6 — 0.302 C. Ex. 3 (d) 8.0 27.664.4 — 0.302 C. Ex. 4 (b) 5.0 52.2 42.8 — 0.362

TABLE 2 Partially Raw material ratio poly- Monomer Ratio of Ratio ofmerized Styrene Methyl elastomeric styrene to Exam- product (partsmethacrylate copolymer methyl ple (parts by by (parts by to monomersmethacrylate No. weight) weight) weight) (by weight) (by weight) Ex. 185 10.0 10.0 4.0/96.0 40.4/59.6 Ex. 2 85 13.0 7.0 4.0/96.0 43.4/56.6 Ex.3 85 5.0 15.0 4.0/96.0 49.0/51.0 C. Ex. 1 85 15.0 5.0 4.0/96.0 45.3/54.7C. Ex. 2 85 13.5 6.5 4.0/96.0 23.0/77.0 C. Ex. 3 85 16.0 4.0 6.5/93.540.2/59.8 C. Ex. 4 85 11.0 9.0 4.0/96.0 55.0/45.0

TABLE 3 Total Vicat Saturated Izod light soften- Exam- water Flexuralimpact transmit- Haze ing ple absorbance modulus strength tance valuepoint No. (%) (MPa) (kJ/m²) (%) (%) (° C.) Ex. 1 0.67 2870 3.3 91.0 0.8102.0 Ex. 2 0.63 2790 5.7 91.2 1.5 103.7 Ex. 3 0.45 2850 4.0 90.7 2.394.0 C. Ex. 1 0.62 2760 3.1 90.5 7.0 97.1 C. Ex. 2 0.93 2080 7.4 91.43.5 106.6 C. Ex. 3 0.67 1790 9.2 91.1 4.2 103.3 C. Ex. 4 0.42 3120 4.189.8 20.2 89.0 C. Ex. 5 0.77 3300 1.6 92.0 0.3 103.0

TABLE 4 Example Deflec- Cracking/ Clearness Thermal No. Warp tionchipping of image deformation Ex. 1 Small Small No Good No Ex. 2 SmallSmall No Good No Ex. 3 Small Small No Good No C. Ex. 1 Small Small NoPoor No C. Ex. 2 Large Small No Good No C. Ex. 3 Small Large No Good NoC. Ex. 4 Small Small No Poor Yes C. Ex. 5 Small Small Yes Good No

Example 4

To 85 parts by weight of a partially polymerized product prepared in thesame manner as in Example 1, were added 10 parts by weight of styrene,10 parts by weight of methyl methacrylate, 0.1 part by weight of 70 wt.% tert-butyl peroxypivalate (a polymerization initiator), 0.3 part byweight of tert-amyl peroxy2-ethylhexanoate (a polymerization initiator)and 0.1 part by weight of tert-dodecylmercaptan (a chain transfer agent). The mixture was charged in each of two cells, which were constructedwith a pair of glass plates and a gasket with a gap distance of 1.8 mmand 2 mm, respectively, and heated in an air oven at 70° C. for 8 hours,then at 75° C. for 2 hours, and further at 120° C. for 1 hour tocomplete the polymerization. Thereby, resin sheets respectively havingthicknesses of 1.8 mm and 2 mm were obtained.

The physical properties of the resin sheet having a thickness of 2 mmwere measured. The saturated water absorption was 0.6%, the flexuralmodulus was 2770 MPa, the notched Izod impact strength was 7.0 kJ/m²,the total light transmittance was 91%, the haze value was 0.3%, and theVicat softening point was 104° C.

A UV-curable resin was charged between the resin sheet having athickness of 1.8 mm and a mold having a Fresnel lens shape, and cured byirradiation of UV-ray to form a Fresnel lens layer having a thickness of100 to 300 μm on the surface of the resin sheet. This sheet was cut byapplying cutting blades from the both sides in a direction substantiallyperpendicular to the surface. As a result, neither cracking nor chippingwas found.

Comparative Example 6

A styrene-methyl methacrylate copolymer (a weight ratio of styrene tomethyl methacrylate=40:60) (MS 600 available from Nippon Steel ChemicalCo., Ltd.) was molded with an extrusion molding machine to obtain aresin sheet having a thickness of 1.8 mm.

A UV-curable resin was charged between this resin sheet and a moldhaving a Fresnel lens shape, and cured by irradiation of UV-ray to forma Fresnel lens layer having a thickness of 100 to 300 μm on the surfaceof the resin sheet. This sheet was cut by applying cutting blades fromthe both sides in a direction substantially perpendicular to thesurface. As a result, many crackings and chippings were found.

Effects of the Invention

The resin composition of the present invention can suitably be used as abase material of a sheet for a screen which has good transparency,suffers from less deformation such as warp or deflection, and is hardlycracked or chipped.

1. A resin composition obtained by copolymerizing a compositioncomprising (A) an elastomeric copolymer which comprises styrenemonomeric units and diene monomeric units, and (B) a copolymer whichcomprises styrene monomeric units and (meth)acrylate monomeric units,the resin compostion having the following properties (1) to (5): (1) asaturated water absorption of 0.8 % or less at a temperature of 60° C.and a relative humidity of 90%; (2) a flexural modulus of at least 1,800MPa; (3) a notched Izod impact strength of at least 2 kJ/m²; (4) a totallight transmittance of at least 85% and a haze value of 5% or less whenproviding a sheet with a thickness of 2 mm; and (5) a Vicat softeningpoint of at least 90° C.
 2. The resin composition according to claim 1,wherein the saturated water absorption is 0.7% or less.
 3. The resincomposition according to claim 1, wherein the flexural modulus is atleast 1900 MPa.
 4. The resin composition according to claim 1, whereinthe notched Izod impact strength is at least 2.5 kJ/m².
 5. The resincomposition according to claim 1, wherein the Vicat softening point isat least 95° C.
 6. An optical screen comprising a resin compositionaccording to any one of claims 1 to 5 as a base material.
 7. A methodfor producing a sheet for an optical screen comprising the step ofcutting a sheet which comprises a resin composition according to any oneof claims 1 to 5 as a base material so as to apply cutting blades to therespective surfaces of the sheet.
 8. The resin composition according toany one of claims 1 to 5, which is obtained by partially polymerizing acomposition containing (A) an elastomeric copolymer which comprisesstyrene monomeric units and diene monomeric units, a styrene monomer, a(meth)acrylate monomer and optional other monomer by bulkpolymerization, and further polymerizing the monomers by castpolymerization or suspension polymerization.
 9. The resin compositionaccording to any one of claims 1 to 5, wherein the amount of theelastomeric copolymer (A) is from 1 to 20% by weight based on the weightof the resin composition, and the amounts of the styrene monomer, the(meth)acrylate monomer and optional other monomer are 25 to 65% byweight, 35 to 75% by weight and 0 to 40% by weight respectively, basedon the total weight of the monomers.
 10. The resin composition accordingto claim 1, wherein the elastomeric copolymer (A) is an elastomericcopolymer prepared by solution polymerization.
 11. The resin compositionaccording to claim 1, wherein the elastomeric copolymer (A) is a randomcopolymer.